1. Field of the Invention
The present invention relates generally to methods and apparatuses which are utilized for the production of ophthalmic lenses, and more particularly, pertains to a method for the removal or demolding of molded ophthalmic contact lenses from the individual molds in which they are produced. Moreover, the invention is also directed to the provision of novel apparatus for implementing the demolding of such ophthalmic lenses, the latter of which may consist of suitable hydrogel contact lenses or other types of high-precision ophthalmic lenses; for example, such as intraocular contact lenses, and wherein the apparatus is especially suited for implementing the inventive lens removal or demolding methods.
The phenomenal growth of the industry which is engaged in the manufacture of the evermore popular ophthalmic contact lenses, especially the aspects of the industry which pertains to the supplying of contact lenses which are intended for frequent periodic replacement by a wearer, has dramatically increased the need for the mass-production of immense quantities of such lenses which are of a consistently high quality while being inexpensive to produce. Consequently, commensurate with the foregoing needs of the industry, this has necessitated manufacturers of such lenses to strive for the development of automated methods and apparatuses which are particularly adaptable to high-speed automated production practices, and which perform with consistency at adequate degrees of accuracy or precision in a highly cost-effective and consequently economically viable manner.
Pursuant to the currently developed technology which is concerned with the production of ophthalmic lenses, particularly such as soft contact lenses of the hydrogel type, there is normally utilized a monomer or monomer mixture which is polymerizable in a plastic mold. Generally, although not necessarily, the material for the ophthalmic contact lenses is selected from a suitable hydrophilic material, preferably a monomer to form a so-called HEMA-based polymer (hydroxyethyl-methacrylate), although other suitable polymerizable monomers may also be employed for the lenses, as discussed further on hereinbelow.
2. Discussion of the Prior Art
Direct molding processes which are typically employed pursuant to the current state-of-the-art for the forming of soft hydrogel ophthalmic contact lenses may be readily found; for example, in the disclosures of U.S. Pat. No. 5,080,839 to Larsen; U.S. Pat. No. 5,039,459 to Larsen et al.; U.S. Pat. No. 4,889,664 to Larsen et al.; and U.S. Pat. No. 4,495,313 to Larsen. As elucidated in the above-mentioned U.S. patents, the processes for the forming of the soft ophthalmic contact lenses may include the steps of dissolving a monomer mixture and a non-aqueous, water-displaceable solvent, and thereafter placing the monomer and solvent mixture in a mold providing a mold cavity which is in the configuration of the finally desired hydrogel contact lens. Subsequently, the monomer and solvent mixture is subjected to physical conditions causing the monomer or monomers to polymerize, thereby producing a polymer and solvent mixture in the shape of the final hydrogel contact lens. After completion of the foregoing procedure, the solvent is displaced with water in order to produce a hydrated lens whose final size and shape are similar to the configuration of the original molded polymer and solvent article.
Basic molds which are utilized for receiving the polymerizable monomer feed material for the forming of the lenses are disclosed, for example, in U.S. Pat. No. 5,094,609 to Larsen; U.S. Pat. No. 4,640,489 to Larsen et al.; and U.S. Pat. No. 4,565,348 to Larsen. Ordinarily; for instance, as disclosed in U.S. Pat. No. 4,640,489, the mold which is employed consists of a two-piece mold having a female mold portion with a generally concave lens surface, and a male mold portion having a generally convex lens surface; and which is adapted to mate with the female mold portion, with both mold portions being preferably constituted of a thermoplastic material, such as polystyrene. As disclosed in the above-mentioned U.S. patent, polystyrene and copolymers thereof is considered to be a preferred mold material inasmuch as it does not crystallize during cooling of the hot melt which is utilized to form the lenses, and consequently exhibits little or no shrinkage when subjected to the processing conditions necessitated during the direct molding process, as discussed hereinabove. Alternatively, there may also be used suitable molds which are constituted of polypropylene or polyethylene; in essence, such as are described in specific detail in the disclosure of U.S. Pat. No. 4,121,896.
During the implementation of the molding process, the monomer and monomer mixture is supplied in an excess amount to the concavity of the concave female mold portion prior to the mating of the female and male mold portions. During the assembly of the male and female mold portions, which would conjointly define therebetween the lens-forming cavity between the concave and convex mold portions of the mold, and also provide for a perimetral lens edge, excess monomer or monomer mixture is expelled or squeezed out from the mold cavity and comes to rest on a flange or between flanges which surround one or both of the mated mold portions. Upon polymerization, this excess material which is derived from the monomer or monomer mixture produces an annular flange or ring of the HEMA-based material which is employed for producing each of the contact lenses so as to extend about the formed lens externally of the mold cavity between the flange structure of the mated male and female mold portions. In accordance with the disclosures of the above-referenced U.S. Pat. Nos. 5,039,459; 4,889,664; and 4,565,348, there is set forth the requirement that the materials for the mold and lens, and the chemistry and physical processes which are implemented during the molding sequence be controlled in a manner whereby the mated mold portions may be readily separated without the necessity for having to apply an undue force, which at times may be necessitated when the molded lens adheres to the lens mold, or in the event that the mated mold portions exhibit a tendency to stick to each other subsequent to the polymerization of the lens material.
Taking the foregoing into consideration, the processes pursuant to the prior art which are employed for separating the mold portions and for removing the molded lens therefrom, essentially comprise a preheating stage, a heating stage, and a physical or mechanical prying open and separating of the mold portions, and thereafter a lens removal procedure. The preheating and/or heating stage employed in the above mold separating and lens removal process contemplates the provision of applying heat to the back mold portion, normally the male or convex mold portion, generally through the application of a heated air stream, by means of convection. Inasmuch as the adhesive force which is present between the molded lens and a mold surface is a function of temperature; in effect, a higher temperature leads to a lower adhesive force. Accordingly, a temperature gradient across the lens can thus be used to keep the lens preferentially adhering to one mold half. This effect is at its greatest in the presence of a maximum thermal gradient.
More recent techniques which have been developed, or are currently in the process of being developed for the achieving of a temperature gradient between the male (back) lens mold portion and the contact lens, include processes involving laser lens demolding technology, such as is described in copending U.S. patent application Ser. No. 08/257,801, now abandoned, which is assigned to the common assignee of the present application; or through the implementation of steam impingement in order to generate the necessary temperature gradient, as described herein and in copending U.S. patent application Ser. No. 08/258,265, pending, which is also assigned to the common assignee of the present application; and wherein the disclosure of the above-identified applications are incorporated herein by reference.
At the present time, the procedure of physically prying apart the mated lens mold portions which contain the polymerized contact lens in a molding cavity which is located therebetween is adapted to be accomplished by the application of mechanical leverage, whereby the leverage or prying action may be implemented automatically from one side of the mated lens mold portions.
For example, the disclosure of U.S. Pat. No. 4,889,664, referred to hereinabove, discloses a test fixture which is employed to measure the forces which are required in order to open or separate the mated mold portions. The test fixture discloses a holding fixture for retaining the bottom half of the lens mold, and a lever structure which is positionable between the top mold half portion and the bottom mold half portion, and which engages the former so as to enable prying the top half mold portion away from the bottom half mold portion at a controlled rate of mold separation. Generally, such lever structure for prying apart the lens mold portions consists of a plurality of prying fingers which engage beneath the flange structure encompassing the upper mold half portion, the latter of which generally defines the back curve of the lens which is being molded, and the vertical lifting force imparted to the upper mold half portion by the therewith engaged prying fingers is normally sufficient to disengage the mating mold portions so as to enable separation thereof and afford access to the contents of the mold cavity; in effect, the molded ophthalmic contact lens. Since the prying is ordinarily effected from one side of the flange structure of the upper or back curve mold half portion, and the opposite side is unsupported, the back mold half portion tends to pivot on the bottom or front curve mold portion so as to squash the material at the edge of the lens contained therebetween. This is potentially a source of possible damage being imparted to the contact lenses during mold separation, rendering the lenses unusable and the lens manufacturing process economically not viable for mass production techniques.